Hasn’t TY-90 got a much smaller engagement envelope than SA-19? TY-90 as an AAM from helicopters has what 7km or there abouts so as a SAM without additional booster, what 5km????

They have several choices, QW-3, QW-4 are among them. And there is the other question of whether it’s better to do that or to put Type 730 and some future VLS version of HH-7 on the same ship. You are going to get much better performance that way.